Polyimides are condensation polymers commonly synthesized by the reaction of aromatic dianhydrides with aromatic diamines. The intermediate poly(amic acid) is either thermally or chemically cyclodehydrated to form the polyimide which has a repeat unit of the general type ##STR1## Ar is a tetravalent aromatic radical which can be as simple as 1,2,4,5-tetrasubstituted benzene. Ar may be a bis-4-(o-diphenylene) having the general structure ##STR2## where X=nil, O, S, SO.sub.2, C=O, Si(CH.sub.3).sub.2, etc., or Ar may be any other appropriate tetravalent radical. Ar' is a divalent aromatic radical which may be 1,3-phenylene, 1,4-phenylene, 4,4'-biphenylene, 4,4'-oxydiphenylene, 4,4'-thiodiphenylene, 4,4'-carbonyldiphenylene, 4,4'-methanediphenylene, or any other appropriate divalent radical.
Synthesis and characterization of polyimides has been extensively reported in the literature. The preparation of aromatic polyimides by reaction of an aromatic dianhydride with an aromatic diamine, followed by thermal cyclization was first reported in 1963 [G. M. Bower and L. W. Frost, Journal of Polymer Science Al, 3135 (1963)]. Several reviews on polyimides have been published [C. E. Sroog, "Polyimides" in Encyclopedia of Polymer Science and Technology, (H. F. Mark, N. G. Gaylord, and N. M. Bikales, Ed.), Interscience Publishers, New York, 1969, Vol. 11, pp. 247-272; N. A. Adrova, M. I. Bessonov, L. A. Lauis, and A. P. Rudakov, Polyimides, Technomic Publishing Co., Inc., Stamford, Conn., 1970].
Wholly aromatic polyimides are known for their exceptional thermal, thermooxidative and chemical resistance. Several polyimides such as Kapton.RTM. (Dupont), PI-2080 (Upjohn), XU-218 (Ciba-Gigy), ULTEM.RTM. (General Electric) and LARC-TPI (Mitsui-Toatsu) are commercially available and used as films, moldings, adhesives, and composite matrices. As a class of materials, aromatic linear polyimides are generally considered to be amorphous. However, there are numerous examples of polyimides which display crystallinity (Adrova, op. cit., pp. 136-144; T. L. St. Clair and A. K. St. Clair, Journal of Polymer Science, Polymer Chemistry Edition, 15, 1529 (1977)). Kapton.RTM., a commercially available polyimide film, has been shown to exhibit molecular aggregration or superstructure (S. Isoda, H. Shimoda, M. Kochi and H. Kambe, Journal of Polymer Science, Polymer Physics Edition, 19, 1293 (1981); S. Isoda, M. Kochi, and H. Kambe, Ibid., 20, 837 (1982)). Kapton.RTM. and the other reported semi-crystalline polyimides exhibit exceptional thermal stability and resistance to solvents while under stress, but cannot be easily thermoformed into useful molded objects or composites.
The introduction of crystallinity into a polymer has long been recognized as an effective means of improving the solvent resistance and increasing the modulus. In addition, if the proper degree and type of crystallinity is attained, the material can also display extremely high toughness. A notable example is polyetheretherketone (PEEK.RTM.) (Imperial Chemicals Industries) which exhibits a very high fracture toughness (C.sub.Ic, critical strain energy release rate) and is highly solvent resistant. PEEK.RTM. can also be thermally processed into moldings and composites. The carbonyl and ether connecting groups between the aromatic rings in PEEK.RTM. tend to be so stereochemically similar that the tendency toward crystalline order is greatly enhanced (T. E. Atwood, P. C. Dawson, J. L. Freeman, L. R. J. Hoy, J. B. Rose and P. A. Staniland, Polymer, 22, 1096 (1981)).
It would be advantageous to extend this unique relationship between carbonyl and ether linkages to other classes of polymers, particularly to polyimides. Polyimides are more easily prepared and isolated than PEEK.RTM.. Additionally, special technology is required for impregnating PEEK.RTM. into fibers due to the insolubility of PEEK.RTM. in common solvents. The poly(amic acid) precursor to polyimides is usually soluble in the reaction mixture and is applied as a solution to fibers or fabric. In this manner good impregnation or "wetting" of the fibers is obtained before thermal cyclodehydration to form an insoluble polyimide. An alternate method involving melt impregnation with the polyimide is also envisioned.
The ratio of carbonyl to ether linkages is critical toward achieving the goal of thermally processable semi-crystalline polyimides. The carbonyl and ether linkages could be incorporated into either the Ar (dianhydride) or the Ar' (diamine) portion of the polyimide repeat unit. However, experience has shown that the diamine portion is easier to modify, resulting in fewer steps than required for the synthesis of new dianhydrides. Novel diamines containing varying rations of carbonyl to ether groups would still have to be synthesized from commercially available materials.
The present invention is a new composition of matter and concerns new polyimides and novel monomers and the process for preparing same.
Another object of the present invention is to provide new polyimides that are useful as adhesives, coatings, films, membranes, and composite matrices.
Another object of the present invention is the synthesis of five new monomers:
1,3-bis(4-aminophenoxy4'-benzoyl)benzene;
1,4-bis(4-aminophenoxy-4-benzoyl)benzene;
4,4'-bis(4-aminophenoxy-4'-benzoyl)bensophenone;
4,4'-bis(4-aminophenoxy-4'-benzoyl)diphenyl ether; and
2,6-bis(4-aminophenoxy-4'-benzoyl)naphthalene.